Prevention of corrosion fatigue failures



Patented Oct. 11, 1 938 UNITED STATED PATENT OFFICE FAIL URES

Frank N. Spoiler, Pittsburgh, Pa., assignor to National Tube JerseyCompany, a corporation of New No Drawing. Application March 24, 1937,Serial No. 132,881

3 Claims.

This invention relates to the operation of repeatedly stressed steelhaving all or a part of its surface immersed in a fluid containing atleast small amounts of oxygen, the primary obiect being to preventcorrosion fatigue failure of the steel or other localized corrosioneffects .of an objectionable nature.

There are various examples of steel operating under the above describedconditions, it being generally recognized that fatigue failure of steelworking in fluid, such as water, containing at least small amounts ofoxygen, are attributable to localized corrosion creating pits wherestress concentrates repeatedly until cracks develop. There yare variousremedies, some contemplating the removal of oxygen from the water andothers the addition of corrosion inhibitors to the water. These schemesare all more or less objectionable because of expense, lack of results,and other factors.

According to the present invention, the trouble under discussion iseliminated, or at least greatly retarded, by the addition of colloids tothe water I or other fluid contacting the surface of the steel.

It has been found that relatively small amounts of colloids, when addedto the fluid containing oxygen, function to keep this oxygen dispersedthroughout the fluid and thusprevent oxygen concentrations, this in turnpreventing the localized corrosion eiiects required to initiate fatiguefailures of the character mentioned. In other words, the invention is amethod of retarding corrosion fatigue failure of steel having a surfaceimmersed in fluid containing oxygen, which ineludes constantly keepingthe oxygen dispersed throughout the fluid to prevent localized corrosionof the steel, by the use of colloids dispersed throughout the fluid toprevent oxygen collections or concentrations.

As little as 2 per cent. colloids produce the above described effect inwater saturated with free oxygen at normal temperature and pressure.Thus it has been found that 2 per cent. of bentonite (nearly 100 percent. collodial clay) 46 in water containing suflicient oxygen tonormally cause the rapid development of corrosion fatigue faflureofrepeatedly stressed steel specimens immersed in this water willgreatly prolong the time before failure occurs under such conditions.

60 Such a small percentage of colloid does not materially alter theviscosity of the fluid. As a result the principles of the invention are,for example, applicable to boiler water. Colloids other than bentoniteclay may be used, provided they are of such a character as to produce acolloidal dispersion evenly throughout the fluid, whereby to hold anyoxygen contained by the fluid in an evenly dispersed condition.

The exact mechanism by which colloids prevent localization of attackunder these condi- 1o tions is not known with certainty but is thoughtto be due to the adsorption of free oxygen on the minute colloidalparticles.

It will'be understood more or less colloidal matter, or other reagentsto prevent localization it of corrosion, must be used to produce thedesired effect depending upon the composition of the fluid and otherfactors.

It is to be understood that the corrosiveness of the fluid containingthe colloidal matter in the 20 absence of stress is only slightlyreduced, but any corrosion resulting from its contact with the steelwill be evenly distributed over the surface of the steel immersed in thefluid, thereby eliminating the condition required for corrosion g5fatigue failure. f

I claim:

1. A method'of retarding corrosion fatigue failure-of steel having arepeatedly stressed surface immersed in fluid containing oxygen,including constantly keeping the oxygen dispersed throughout the fluidto prevent localized corrosion of the steel.

2. A method of retarding corrosion fatigue failure of steel having arepeatedly stressed surface 35 immersed in fluid containing oxygen,including constantly keeping the oiwgen dispersed throughout the fluidto prevent localized corrosion of the steel by the use of colloidsdispersed throughout the fluid to prevent oxygen collections. 40

3. A method of retarding corrosion fatigue failure of steel having arepeatedly stressed surface immersed in fluid containing oxygen,including constantly keeping the oxygen dispersed throughout the fluidto prevent localized corrosion of the steel by the use of about 2 percent. or more (:01- loids dispersed throughout the fluid to preventoxygen collections.

FRANK N. SPEILER. 5o

